Idiopathic interatitial pneumonia (IIP) comprises a heterogeneous spectrum of clinicopathological disease entities such as idiopathic pulmonary fibrosia (IPF) the histology of which is diagnosed as usual interstitial pneumonia (DIP), nonspecific interstitial pneumonia (NSIP), desquamative interstitial pneumonia (DIP), respiratory bronchiolitis associated interstitial lung diseases (RB-ILD), bronchiolitis obliterans organizing pneumonia (BOOP), acute interstitial pneumonia (AIP), andlysiphocytic interstitial pneumonia (LIP). Interstitial pneumonia associated with collagen vascular diseases (IP-CVD) are candidate for differentiation to IIP. Among the IIPs, the DIP-histology relates to an unfavorable prognosis, however, in the cases of DIP-CVD, histological features are not likely to relate to prognosis. In order to investigate a difference between idiopathic cases and CVD with UIP-histology, or with NSIP-histology,clinicopathological features were compared between IPP/UIP and UIP-CVD.An increase in BAL fluid lymphocytes was found in patients with UIP-CVD, but not in patients with IPF/UIP. This differences may relate to a difference in the degree of fibrosis ; those in patients with UIP-CVD were milder than those in patients with IPF/UIP. It remains to be examined whether a BAL fluid lymphocytosis plays a role of regulating a development of pulmonary fibrosis. Differences in the nature of pulmonary fibrosis can be found between the DIP-histology and the NSIP-histology in the idioapthic cases. It also will be examined whether a similar difference can be shown in the cases associated with CVD.